Reflection type display apparatus and method for manufacturing light guide plate

ABSTRACT

A reflection-type display apparatus that includes cavities dispersed on a light guide plate and is a type of flexible thin film, and a method for manufacturing a light guide plate. The reflection-type display apparatus includes: a reflection-type display; a light source provided on one side of the reflection-type display; a light guide plate bonded to the upper surface of the reflection-type display to scatter light introduced from the light source and having cavities transversely and longitudinally disposed by predetermined intervals on the upper surface thereof; and a film bonded to the upper surface of the light guide plate to protect the upper surface of the light guide plate.

CLAIM OF PRIORITY

This application claims priority from an application entitled“REFLECTION TYPE DISPLAY APPARATUS AND METHOD FOR MANUFACTURING LIGHTGUIDE PLATE” filed in the Korean Intellectual Property Office on Nov.28, 2007 and assigned Serial No. 2007-0121905, the contents of which areincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a reflection type displayapparatus and a method for manufacturing a light guide plate. Moreparticularly, the invention relates to a reflection type display in theform of a thin film that can be used in an electronic paper display.

2. Description of the Related Art

In general, an electronic paper display apparatus displays an image bymoving black and white dyes using electric fields and is suitable foruse in an information terminal due to its low power consumption. Such anelectronic paper display apparatus is a reflection type displayapparatus through which light cannot pass due to its materialcharacteristics.

As mentioned above, unlike a liquid crystal display, (i.e. arepresentative transmission type display), since light cannot passthrough such a reflection type display apparatus, the reflection typedisplay apparatus cannot employ an illumination unit such as a backlight unit located on the rear surface of a display to directlyilluminate the display. The reflection type display cannot secure nightvisibility, and uses a front light unit (FLU) for illumination. In otherwords, a reflection type display displays an image even without usingany light source at a place where an external light source is connectedthereto, and displays an image by illumination of an FLU at a placewithout any external light source.

The structure of an FLU of a conventional reflection type displayapparatus is illustrated in FIG. 1. FIG. 1 provides a perspective viewthat schematically illustrates an FLU structure of a conventionalreflection type display apparatus.

Referring now to FIG. 1, a conventional FLU includes a light source 103creating and emitting light, a light guide plate 107, a light bar 101for introducing the light emitted from the light source 103 into thelight guide plate 107. The light guide plate 107 scatters the introducedlight.

The light guide plate 107 is provided on the upper surface of thereflection type display 109, and V-shaped grooves are formed on theupper surface of the light guide plate 107. The grooves having aspecific angle are linearly or curvedly disposed in the longitudinaldirection of the light guide plate 107 and are disposed transversely bya predetermined angle according to a predetermined rule.

If the introduced light reaches the V-shaped grooves, it is reflected bya specific angle according to the angle of the grooves and thedifference in indices of refraction between the light guide plate 107and the exterior. When the angle of the reflected light does not satisfythe condition of total reflection, the light travels outside the lightguide plate 107. The light traveling outside the light guide plate 107is reflected by the reflection type display 109 again and reaches theeyes of a user. When the grooves are distributed over the upper surfaceof the light guide plate 107, the entire light guide plate 107 isilluminated. The reference numeral 105 indicates a protection filmand/or a key film for protection of the light guide plate 107 orformation of keys.

The FLU requires the light bar 101 to introduce the light into the lightguide plate 107. Minute grooves (not shown) are formed in the light bar101. The grooves of the light bar 101 change the direction of the lighttraveling out of the light source 103 and uniformly introduce the lightthrough a side surface of the light guide plate 107. In other words, thelight bar 101 converts a point light source to a line light source. Inparticular, when the light source 103 is a light emitting diode (LED),the light bar 101 is essential.

Meanwhile, the light guide plate is manufactured through injectionmolding or mechanical machining. More particularly, the light guideplate is made of an optically transparent material, such as plastic,through injection molding using a mold having V-shaped grooves, or ismade by directly machining V-shaped grooves.

However, it is difficult to form grooves in a light guide plate in athin film because the material is extremely thin. Also, as reflectiontype display in the form of a thin film have become increasinglypopular, it is not preferable to form grooves in the thin film inaddition to being difficult to implement. In particular, a reflectiontype display applied to applications such as a keypad requiring highflexibility requires a thickness of below 0.2 mm, which is impossibleusing a conventional technology for manufacturing a light guide plate.

Furthermore, since a high-priced mold is used or a mechanical method oflow productivity is used in a conventional technology for manufacturinga light guide plate, the price of an FLU increases.

In addition, since there exists sharp border surfaces in V-shapedgrooves applied to an FLU due to their characteristics, a user may seethe grooves when there is no illumination.

SUMMARY OF THE INVENTION

The present invention provides a thin film shaped reflection-typedisplay apparatus and a method for manufacturing a light guide plate.

The present invention also provides a low-priced reflection-type displayapparatus whose cavities can be rarely seen and a method formanufacturing a light guide plate.

The present invention also provides a reflection-type display apparatuswhose cavities are transversely and longitudinally disposed on the uppersurface of a light guide plate and a method for manufacturing a lightguide plate.

In accordance with an exemplary embodiment of the present invention,there is provided a reflection-type display apparatus comprising: areflection type display; a light source provided on one side of thereflection type display; a light guide plate bonded to the upper surfaceof the reflection type display to scatter light introduced from thelight source and having cavities transversely and longitudinallydisposed by predetermined intervals on the upper surface thereof; and afilm bonded to the upper surface of the light guide plate to protect theupper surface of the light guide plate.

The present invention includes a method for manufacturing a light guideplate of a reflection-type display apparatus, the method comprising:manufacturing a mask in a pattern having predetermined size andinterval; lithographing cavities in a master stamper by an exposureprocess and a development process through use of the mask and formingcavities by an etching process; plating nickel on the master stamper andmanufacturing a stamper having embossments by removing the masterstamper; and forming cavities by pressing and/or heating the material ofthe light guide plate using the stamper.

According to the present invention, a thin film shaped reflection-typedisplay apparatus is provided by manufacturing a thin film shapedflexible FLU whose cavities can not be seen. In other words, a usercannot see the cavities.

Furthermore, a high-priced mold can be excluded by using a stamper toform the cavities, so as to permit a lower-priced FLU to be manufacturedas compared with conventional FLUs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view schematically illustrating an FLU structureof a conventional reflection type display apparatus;

FIGS. 2A and 2B are a perspective view and a sectional viewschematically illustrating an FLU structure of a reflection type displayapparatus according to an exemplary embodiment of the present invention;

FIGS. 3A and 3B are views illustrating an application of the FLU of thereflection type display apparatus according to the exemplary embodimentof the present invention and functions of intervals of cavitiesaccording to the embodiment of the present invention;

FIG. 4 is a flowchart schematically illustrating a method formanufacturing a light guide plate of the reflection type displayapparatus according to the exemplary embodiment of the presentinvention;

FIGS. 5A to 5G are sectional views schematically illustrating a processof manufacturing the light guide plate of a reflection type displayapparatus according to the exemplary embodiment of the presentinvention;

FIGS. 6A and 6B are photos of cavities formed in the process ofmanufacturing a light guide plate of the reflection type displayapparatus; and

FIG. 7 is a drawing of a terminal to which a reflection type displayapparatus according to the exemplary embodiment of the present inventionis applied.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings so thatthose skilled in the art can easily carry out the present invention. Inthe detailed description of the exemplary embodiment of the presentinvention, technologies that are well known in the art and are notdirectly relevant to the present invention will be omitted so as not toobscure appreciation of the subject matter of the present invention by aperson of ordinary skill in the art.

Likewise, in the accompanying drawings, some elements may be omitted, orschematically illustrated, and the sizes of the elements do not reflecttheir actual sizes for explanatory purposes.

FIGS. 2A and 2B are a perspective view and a sectional viewschematically illustrating an FLU structure of a reflection type displayapparatus according to an embodiment of the present invention.

Referring now to FIGS. 2A and 2B, the reflection type display apparatusaccording to the exemplary embodiment of the present invention includesa reflection type display 209, a light source 203 provided on one sideof the reflection type display 209, a light guide plate 207 bonded tothe upper surface of the reflection type display 209, and a film 205bonded to the upper surface of the light guide plate 207. In this case,the light source 203 and the light 207 constitute an FLU of the presentinvention.

The light source 203 creates and emits light. The light source 203 ispreferably provided on one side of the reflection type display 209. Thelight source 203 may be a light emitting diode (LED) or a cold cathodefluorescent lamp (CCFL). Two light sources 203 are illustrated in thedrawing, but the present invention is not limited thereto. The number oflight sources 203 may be changed according to the size of the reflectiontype display 209. The FLU according to the exemplary embodiment of thepresent invention does not need a light bar that was required in theprior art due to cavities 217 of the light guide plate 207 that will bedescribed later.

A minimum interval is provided between the light source 203 and thelight guide plate 207 to increase light introduction efficiency.Considering tolerances in an existing assembling process, the intervalbetween the light source 203 and the light plate 207 is preferably below0.2 mm.

Still referring to FIGS. 2A and 2B, the light guide plate 207 scattersthe light introduced from the light source 203. The light guide plate207 is bonded between the upper surface of the reflection type display209 and the lower surface of the film 205. The light guide plate 207 isbonded using a highly transparent adhesive or a bonding tape. The lightguide plate 207 has a high transparency and is made of plastic such as,for example, polyvinyl chloride (PC), polyethylene terephthalate (PET),polymethylmethacrylate (PMMA), or polyurethane (PU), or silicon.

In the case of an inflexible light guide plate 207, the thicknessthereof is preferably about 0.1 to 0.4 mm, and otherwise, 0.1 to 0.2 mm.The flexible light guide plate refers to a light guide plate whosereflection type display apparatus is used as a keypad that can beclicked. In other words, the flexible reflection type display apparatusincludes keys that can be pressed by a user. The minimum thickness ofthe light guide plate 207 is preferably 0.1 mm, whereby the light guideplate guarantees the brightness of 10 nit (nit is a unit of luminance inthe MKS unit system and is a brightness of a surface having a lightintensity of 1 cd/m2 or 10-4 sb) that is a reference brightness commonlyused in the field.

As shown in the example in FIG. 2A, cavities 217 are disposed bypredetermined intervals on the upper surface of the light guide plate207 that is bonded to the film 205. When light is introduced into thelight guide plate 207, the light is guided within the light guide plate207 by the total reflection condition. The guided light reaches a cavity217, the total reflection condition is broken, whereby some light isrefracted to travel out of the light guide plate 207 and some light isreflected to be guided into the light guide plate 207 until it reachesthe next cavity 217. In other words, the light introduced into the lightguide plate 207 is scattered by the cavities according to its guideddistance and is used in illumination.

The cavities 217 are dispersed transversely and longitudinally on theupper surface of the light guide plate 207, so that illumination ofuniform brightness can be made over the entire surface of the lightguide plate 207. As the cavities 217 are closer to the light source 203,the intervals between the cavities 217 are preferably smaller, and viceversa. This will be described in detail with reference to FIGS. 3A and3B. FIGS. 3A and 3B are views illustrating an application of the FLU ofthe reflection-type display apparatus according to the exemplaryembodiment of the present invention, and the functions of intervalsbetween cavities according to the exemplary embodiment of the presentinvention.

The intervals between the cavities 217 need to be regulated to obtainuniform illumination. In other words, the densities of the cavities 217,i.e. the numbers of cavities 217 per unit area are regulated to controldistribution of brightness according to the distances between the lightsource 203 and the cavities 217. The sizes or depths of the cavities 217may be regulated, in which case as the sizes or depths of the cavities217 increase, the cavities 217 may be undesirably easily seen. Theintervals between the cavities 217 is varied according to their distancefrom the light source 203 and the cavities have a polynomialdistribution expressed in Formula 1.

y=Ax ⁴ +Bx ³ +Cx ² +Dx+E  Formula 1

where y represents intervals between the cavities 217, and x representsdistances between the light source 203 and the cavities 217, and A, B,C, and D are properly selected according to the size and shape of thelight guide plate 207. In Formula 1, as the distances between the lightsource 203 and the cavities 217 become larger, the intervals between thecavities 217 become smaller.

As illustrated in FIG. 3A, the cavities 217 are transversely andlongitudinally disposed in the light guide plate 207. The intervalfunctions of the cavities 217 in the light guide plate 207 are asillustrated in FIG. 3B. As illustrated in FIG. 3B, as the distancesbetween the light source 203 and the cavities become smaller, theintervals between the cavities 217 become larger.

Preferably, the cavities 217 are curved. In other words, the cavities217 have semi-spherical or conic shapes (refer to FIG. 6B). The cavities217 have diameters in this exemplary embodiment of about 30 to 50 μm anddepths of about 3 to 10 μm whereby the cavities are minimally seen andthe brightness of illumination is secured.

The film 205 is provided to protect the light guide plate 207 and form akey. The film 205 may be a protection film or a key film, and may beformed by integrating a protection film and a key film.

Hereinafter, a method for manufacturing an FLU for a reflection-typedisplay according to an exemplary embodiment of the present inventionwill be described in detail. FIG. 4 is a flowchart schematicallyillustrating exemplary steps for manufacturing a light guide plate ofthe reflection-type display apparatus according to the exemplaryembodiment of the present invention. FIGS. 5A to 5G are sectional viewsschematically illustrating a process of manufacturing the light guideplate of a reflection type display apparatus according to the exemplaryembodiment of the present invention.

Referring now to FIGS. 4 and 5A to 5G, the preferred method formanufacturing a light guide plate in a reflection type display apparatusaccording to the exemplary embodiment of the present invention uses astamper. In the particular example, as illustrated in FIG. 4, a mask ismanufactured so as to have a pattern shape having a specific size and aspecific interval (S401). In this case, the shape of the pattern has aspecific shape to form cavities. In other words, the mask ismanufactured such that the diameters of the cavities finally formed inthe light guide plate are 30 to 50 μm and the depths thereof are 3 to 10μm, the cavities are curved, and the intervals between cavities aredefined in FIG. 1.

Thereafter, the cavities are lithographed in a master stamper by anexposure process and a development process through use of the mask(S403). The screens showing the performance of the processes areillustrated in FIGS. 5A and 5B. As illustrated in FIG. 5A, the mask 503manufactured in step S401 is positioned on the master stamper 510, andlight such as ultraviolet (UV) rays is projected to the mask 503 toclassify the mask into necessary and unnecessary sections, whereby aphotoresist (PR) 505 is hardened and an exposure process is carried out.In this case, the master stamper 510 includes a base 507 and aphotoresist 505 located on the base 507. Thereafter, as illustrated inFIG. 5B, a development process in which a section of the photoresist 505of the master stamper that has not been hardened due to failure insupply of the UV rays is removed is carried out.

Thereafter, the cavities are formed in the master cylinder by an etchingprocess (S405). The screen showing the performance of the process isillustrated in FIG. 5C. As illustrated in FIG. 5C, the master stamper520 having the cavities 521 is manufactured through the etching process.In this case, the depths and shapes of the final cavities are determinedaccording to etching degree. The cavities have spherical or conic shapesso that the surfaces of the cavities are curved. The cavities 217 havediameters of 30 to 50 μm and depths of 3 to 10 μm whereby the cavitiesare minimally seen and the brightness of illumination is secured.

Thereafter, the master cylinder is plated with nickel (Ni) (S407). Thescreen showing the performance of the process is illustrated in FIG. 5E.A stamper 530 having embossments as illustrated in FIG. 5E ismanufactured by removing the master stamper 520 with the master stamper520 being plated with nickel as in FIG. 5D. The picture of theembossments are illustrated in FIG. 6A. FIG. 6A is a picture ofembossments formed in the process of manufacturing the light guide plateof the reflection type display apparatus according to the embodiment ofthe present invention.

Still referring to FIG. 4, thereafter, cavities are formed in the lightguide plate by pressing and heating the material of the light guideplate using the stamper (S411). The screen showing the performance ofthe process is illustrated in FIGS. 5F and 5G. As illustrated in FIG.5F, the stamper 530 having the embossments presses and heats thematerial 535 of the light guide plate. Then, a pressure of 5 to 6 MPaand a temperature of 180 to 200 degrees Celsius are applied. The lightguide plate 207 may have a high transparency and may be made of plasticsuch as polyvinyl chloride (PC), polyethylene terephthalate (PET),polymethylmethacrylate (PMMA), or polyurethane (PU), or silicon.

As illustrated in FIG. 5G, the light guide plate 540 having the cavities541 is finally manufactured. The picture of the cavities is illustratedin FIG. 6B. FIG. 6A is a photo of the embossments formed in the processof manufacturing the light guide plate of the reflection-type displayapparatus according to the processed described hereinabove.

Thereafter, although not illustrated, the light guide plate 540 havingthe cavities 541 is machined so as to have a thickness of 0.1 to 0.4 mm.As mentioned above, in the case of an inflexible light guide plate 207,the thickness thereof is 0.1 to 0.4 mm, and otherwise, 0.1 to 0.2 mm.

Hereinafter, the evaluation result of the characteristics of thereflection type display apparatus according to the embodiment of thepresent invention will be described. FIG. 7 is a drawing of one type ofa terminal to which the reflection-type display apparatus according tothe exemplary embodiment of the present invention can be applied.

As illustrated in FIG. 7, the reflection display apparatus applied to aterminal is measured by using a luminance measurer in a dark room. Themeasurement result shows a uniformity of above 50% and a brightness ofabove 10 nit and the cavities cannot be seen.

The reflection-type display apparatus and the method for manufacturing alight guide plate according to the present invention are not limited tothe above-mentioned embodiments, but may be variously modified withinthe spirit of the present invention. Any person skilled in the art canunderstand that various changes and modifications may be made.

1. A reflection-type display apparatus comprising: a reflection-typedisplay; a light source provided on the reflection-type display; a lightguide plate bonded to an upper surface of the reflection-type displayfor scattering light introduced from the light source and havingcavities transversely and longitudinally disposed therein atpredetermined intervals along an upper surface of the light guide plate;and a film bonded to the upper surface of the light guide plate forprotecting the upper surface of the light guide plate.
 2. The reflectiontype display apparatus of claim 1, wherein the cavities have surfaceswhich are curved.
 3. The reflection type display apparatus of claim 2,wherein the diameters of the cavities comprise a range of 30 to 50 μmand the depths thereof comprise a range of 3 to 10 μm.
 4. The reflectiontype display apparatus of claim 1, wherein the thickness of the lightguide plate comprises a range of 0.1 to 0.4 μm.
 5. The reflection typedisplay apparatus of claim 1, wherein when the intervals between thecavities are expressed as y, wherein y has a polynomial distribution of:y=Ax ⁴ +Bx ³ +Cx ² +Dx+E wherein y represents intervals between thecavities, and x represents distances between the light source and thecavities, and A, B, C, and D are selected according to a size and shapeof the light guide plate.
 6. The reflection type display apparatus ofclaim 5, wherein as the distances between the light source and thecavities become larger, the intervals between the cavities becomesmaller.
 7. The reflection type display apparatus of claim 1, whereinthe film comprises at least one of a protection film, a key film, and afilm in which a protection film and a key film are integrated.
 8. Thereflection display apparatus according to claim 1, wherein the lightguide source is arranged adjacent a side of the reflection-type display.9. A method for manufacturing a light guide plate of a reflection typedisplay apparatus, the method comprising: manufacturing a mask in apattern having a predetermined size and interval; lithographing cavitiesin a master stamper by an exposure process and a development processusing the mask, and forming cavities by an etching process; platingnickel on the master stamper and manufacturing a stamper havingembossments by removing the master stamper; and forming cavities bypressing and/or heating the material of the light guide plate using thestamper.
 10. The method of claim 9, wherein in the forming cavitiesstep, a pressure comprising a range 5 to 6 MPa and a temperaturecomprising a range of 180 to 200 degrees Celsius are applied.
 11. Themethod of claim 9, wherein in the pattern of the mask, when theintervals between the cavities are expressed as y, y has a polynomialdistribution of:y=Ax ⁴ +Bx ³ +Cx ² +Dx+E wherein y represents intervals between thecavities, and x represents distances between the light source and thecavities, and A, B, C, and D are selected according to a size and shapeof the light guide plate.
 12. The method of claim 9, further comprising,after forming cavities in the light guide plate, machining the lightguide plate such that the thickness thereof comprising a range of 0.1 to0.4 mm.